1. Field of the Invention
This invention relates to automatic power transmissions providing a plurality of gear reduction ratios, such as automatic mechanical transmissions, and to control systems therefor In particular, the present invention relates to control systems for vehicles with throttle controlled engines and automatic transmissions wherein gear selection and shift decisions are made and executed based upon measured and/or calculated parameters such as output shaft or vehicle speed, input shaft or engine speed, throttle position, calculated engine speed in a potentially engageable ratio, and the like. More particularly, the present invention relates to automatic transmission control systems of the type described above having means to adjust the shift point profiles in response to the direction of the last shift and means to reset the profiles to the normal positions thereof upon the occurrance of one of more predetermined events such as engine speed being greater than a maximum reset value and/or less than a minimum reset value, the passage of predetermined period of time, etc., wherein the engine speed reset values are functions of measured and/or calculated parameters which provides a control logic which is more responsive to actual conditions at the time of and subsequent to the last shift.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, direction of the last shift, and the like are known in the prior art. Examples of such automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048; 4,208,929; 4,039,061; 3,974,720 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
Electronic transmission controls are discussed in a technical paper titled "The Automation of Mechanical Transmissions" by Holmes, Smyth and Speranza at Pages 11-23 of Section IX of the published proceedings of a joint IEEE/SAE "International Congress on Transportation Electronics", IEEE Catalog No. 84CH 1988-5, the contents of which are hereby incorporated by reference.
As may be seen by reference to above-mentioned U.S. Pat. No. 4,361,060, to avoid undesireably rapid downshifts after an upshift, or undesireably rapid upshifts after a downshift (i.e. "hunting"), it is known to adjust or modify the shift points or shift profiles after a shift by increasing the upshift engine speed after a downshift and/or decreasing the downshift engine speed after an upshift. It is also known that the shift points or profiles should be reset to their normal positions to achieve desired vehicle operation as quickly as possible after the likelihood of hunting has been minimized. In U.S. Pat. No. 4,361,060, the shift profiles are reset in two increments, one related to the passage of time and the other to engine speed "passing through" a reset engine speed (i.e. going from greater than to less than, or going from less than to greater than, the reset engine speed). The reset engine speed (see line RR in FIG. 10 of U.S. Pat. No. 4,361,060) was the same regardless of the last engaged gear ratio or vehicle (or engine) speed at the time of the last shift.
While the above referenced automatic transmission control system, as defined in U.S. Pat. No. 4,361,060, is very effective to control an automatic transmission by selecting a desired gear ratio which will tend to optimize the fuel economy and/or performance of the vehicle in view of the sensed parameters and then to command a shift into the selected gear ratio, such control systems were not totally satisfactory. In particular, such control systems were not totally satisfactory as the portion of reset of the shift profiles to the normal positions thereof from the direction of last shift offset related to engine speed was not highly responsive to the last engaged gear ratio, the conditions immediately before and after the last shift and the vehicle performance subsequent to the last shift.